Crown boiler dhw

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H

handyworx

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Jun 11, 2011
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Location
ashford, ct
Installed a Crown Maui combi gas boiler. Works fine except the dhw in the shower fluctuates from hot to lukewarm about every 30 seconds. I did install a Watts MMV mixing valve, but it doesn't make much difference. Is this normal for these units? Anyone have the same experience?
 
Maybe I read that wrong, did you install the mixing valve after you noticed the problem? Either way, a mixing valve is not the solution. Try throttling down the volume in the shower, if the temp stays consistent, I think you're exceeding the demand for that unit.

Here are some other ideas:

1.) Does your unit have a light or display that will flash you a code? If so you should have a manual with the codes on it.

2.) Turn the water off to your house, take the shower valve apart and look for debris.

3.) I think there is a diverter inside the unit, it may be bad or have debris in it.
 
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I installed it after the problem, yes, and after Crown told me to install one. I tried throttling down the shower, no difference. You're probably right, the boiler is only rated for about 3 gals minute. It's not bad in the shower, the owner will just need to get used to it. It's the one he wanted.
 
My first experience like this was with a 1st generation Tankless WH. When the homeowner would use the tub, the hot side would go cold after a second or two. Every other fixture in the home worked fine, even when multiple fixtures were calling for Hot. No other fixtures in the home produced hot when the tub called for hot. I even shut off all the tub/shower and shower valve shut/offs to eliminate the possibility of a cross connection through the shower valve. My best guess was that they were exceeding the demand, because when I throttled down the hot side handle on the tub, it stayed hot.
 
What bothers me is the fact that the boiler fires on and off while calling for hot water. I thought the fire was supposed to be modulated based on the water temp. I'm going to call Crown back on monday about it. It's when the boiler shuts off after reaching around 120 degrees the lukewarm water starts flowing, until it fires again. Not sure if a storage tank would help.
 
If the supply sensor (I think that's what they call it) works and the heat exchanger works (which if they didn't there should be a code) then it simply has to be exceeding the demand.

Why the heck did Crown tell you to put a mixing valve in? I'm genuinely curious to know why the rep went there? I mean these guys/gals deal with this stuff all day, every day so maybe I can learn something here.
 
Actually, it was the guy in tech support at Crown headquarters that told me to install a mixer. No error codes from the unit. Even if I throttle the hot way down, there is still the lag in the temp at the shower head. Another thing I told him was that no matter where I set the dhw thermostat, the boiler gauge shows around 140-150, fluctuating 10-15 degrees as the fire shuts down. He told me to check and see if the wiring to the thermostat was OK, which it is. Could be the supply sensor....
 
With the shower throttled down it equals the demand of any Kitchen sink or even a Lav, so if the same thing doesn't happen with those fixtures, I'm at a loss. Other than the shower valve itself it can only be these things (I think):

1.) Supply Sensor
2.) Heat Exchanger
3.) Diverter (inside the unit)

I forgot the diverter in my last post, but I think a bad diverter can cause a fluctuation.

It makes sense that Crown would tell you to put in a mixing valve because it simply couldn't be a prob with their unit;)
 
It does happen at other fixtures too. Been reading about flow restrictors. Think it may be a good idea to put one of those in? Still calling Crown first thing monday.
 
The tank also has about a 75 degree temp. rise @ approx. 2.5 gpm. If the ambient water temp coming into the house in Ashford, CT is 60 degrees then you will get about enough hot water for a shower only. Any additional fixtures will create too much draw for the unit to keep up. In the winter, as the soil chills, you may have less usable volume.
 
Sorry, checking the temp charts for your area, the average ambient temp is about 45-50 degrees. The last time that I saw an issue with a tankless that involved heating then cooling of the flowing water, it was a bad flow sensor. I guess you'll get more insight on Monday.
 
Actually, I'm working on a house on the Jersey shore. That's where this boiler is installed. I live in Ashford, CT.... but been here since new years.

BTW, flow rate from my tub is 3.5 GPM. The boiler is rated for 2.67 GPM
 
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